Effect of injection of a GnRH analogue at the onset oestrus on LH and FSH release and embryonic mortality in gilts.

In the 1st of 2 experiments, 5 gilts were injected with saline at the onset of standing oestrus (control oestrus), and at the next cycle the same gilts were injected with 100 mu g GnRH analogue. The LH and FSH peaks in the GnRH-treated oestrus were not significantly different from those in the control oestrus, but both peaks were sharper in the GnRH-treated oestrus. In the 2nd experiment, 49 gilts were injected with 100 mu g GnRH at the onset of standing oestrus or were not treated (controls), and slaughtered on day 4, 11, 13 or 35 of pregnancy. For animals slaughtered on day 4, 11 or 13, compared with controls, treated animals had significantly more corpora lutea (16.3 or-2.3 vs. 14.8 or-1.5) and embryos (15.0 or-3.0 vs. 12.1 or-3.4). Embryonic mortality on day 35 was 24.7% in the treated group vs. 11.3% in controls. The av. number of corpora lutea for gilts slaughtered on all 4 days was greater in treated gilts than in controls (16.4 or-2.3 vs. 14.3 or-3.3), but the difference was not significant. A similar trend was observed for number of embryos (15.4 or-2.0 vs. 13.0 or-3.3).